【正文】 nd brakes use the same general procedure. The following step are necessary: 1. Assume or determine the distribution of pressure on the frictional surfaces. 2. Find a relation between the maximum pressure and the pressure at any point 3. Apply the condition of statical equilibrium to find (a) the actuating force, (b) the torque, and (c) the support reactions. Miscellaneous clutches include several types, such as the positivecontact clutches, overloadrelease clutches, overrunning clutches, magic fluid clutches, and others. A positivecontact clutch consists of a shift lever and two jaws. The greatest differences between the various types of positive clutches are concerned with the design of the jaws. To provide a longer period of time for shift action during engagement, the jaws may be ratchetshaped, or geartoothshaped. Sometimes a great many teeth or jaws are used, and they may be cut either circumferentially, so that they engage by cylindrical mating, or on the faces of the mating elements. Although positive clutches are not used to the extent of the frictionalcontact type, they do have important applications where synchronous operation is required. Devices such as linear drives or motoroperated screw drivers must run to definite limit and then e to a stop. An overloadrelease type of clutch is required for these applications. These clutches are usually springloaded so as to release at a predetermined toque. The clicking sound which is heard when the overload point is reached is considered to be a desirable signal. An overrunning clutch or coupling permits the driven member of a machine to “freewheel” or “overrun” because the driver is stopped or because another source of power increase the speed of the driven. This type of clutch usually uses rollers or balls mounted between an outer sleeve and an inner member having flats machined around the periphery. Driving action is obtained by wedging the rollers between the sleeve and the flats. The clutch is therefore equivalent to a pawl and ratchet with an infinite number of teeth. Magic fluid clutch or brake is a relatively new development which has two parallel magic plates. Between these plates is a lubricated magic powder mixture. An electromagic coil is inserted somewhere in the magic circuit. By varying the excitation to this coil, the shearing strength of the magic fluid mixture may be accurately controlled. Thus any condition from a full slip to a frozen lockup may be obtained. 。 that is ,a righthand driver goes with a righthand driven. In the design of crossedhelical gears, the minimum sliding velocity is obtained when the helix angle are equal. However, when the helix angle are not equal, the gear with the larger helix angle should be used as the driver if both gears have the same hand. Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they pletely wrap around the pitch cylinder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angularvelocity reduction between nonintersecting shafts which are usually at right angle. The worm gear is not a helical gear because its face is made concave to fit the curvature of the worm in order to provide line contact instead of point contact. However, a disadvantage of worm gearing is the high sliding velocities across the teeth, the same as with crossed helical gears. Worm gearing are either single or double enveloping. A singleenveloping gearing is one in which the gear wraps around or partially encloses the worm.. A gearing in which each element partially encloses the other is, of course, a doubleenveloping worm gearing. The important difference between the two is that area contact exists between the teeth of doubleenveloping gears while only line contact between those of singleenveloping gears. The worm and worm gear of a set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm